Three-dimensional transmission electron microscopy (3DEM) is emerging as a powerful method for determining the three-dimensional structures of large biological assemblies in solution and in the cell, enabling elucidation of complex biological interactions that are integral to understanding the inner workings of cellular machinery, and yielding novel insights into fundamental biological processes. Hundreds of 3DEM experiments are now reported in the literature each year and more than 1,300 structures are available in public archives through EMDataBank (EMDataBank.org). The major goal of this project is to establish methods to assess the reliability of these structures and to create uniform standards for data exchange, in order to bridge the current substantial gap between 3DEM and established structure determination methods (X-ray crystallography and NMR) in the ability to evaluate and interpret the experimental results. EMDataBank will take a leadership role in facilitating the processes necessary to assess, establish, and disseminate validation methods and data standards. The approach will leverage the expertise and experience of the EMDataBank team in validation, standards, and 3DEM methods development. Validation methods for both 3DEM maps and map-derived models will be established using our own test data sets and software packages as well as those contributed by other electron microscopists. Our results will be made publicly available for comment and review on the EMDataBank website. The PDB exchange dictionary will be extended to support 3DEM community-reviewed validation procedures. Map and map-derived model validation procedures developed through this project will be integrated into the deposition and annotation pipeline of the Protein Data Bank. The work is expected to have a strong transformative impact on both the 3DEM and the wider bioscience communities, enabling independent assessment and interpretation of 3DEM experimental results by both expert and non-expert scientists, and leading to higher reliability and improved consistency of 3DEM structure data.